Asteroid 16 Psyche, once thought to be a metallic core of an early planet, may instead be a pile of rubble held together by gravity, according to new research.
The findings, published in the journal Nature Astronomy, could have implications for our understanding of how planets form.
"We used to think that Psyche was the exposed core of a protoplanet that was about the size of Mars," said lead author Dr. Tracy Becker, a research scientist at the Southwest Research Institute in Boulder, Colorado. "But our new data suggest that it's more likely a pile of debris that was never able to fully coalesce into a planet."
Psyche is about 210 miles (340 kilometers) in diameter and orbits the Sun between Mars and Jupiter. It is one of the most massive objects in the asteroid belt, and it is thought to be the remnant of a protoplanet that was disrupted early in the history of the solar system.
Scientists have been studying Psyche for decades, but they have not been able to get a clear picture of its composition. Some studies have suggested that it is made of metal, while others have suggested that it is made of rock.
The new research, which used data from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, provides strong evidence that Psyche is not made of metal.
"The ALMA data show that Psyche is not emitting any thermal radiation," said Becker. "This means that it is not a good conductor of heat, which is consistent with it being a pile of rubble."
The findings have implications for our understanding of how planets form. Scientists believe that planets form when small pieces of rock and dust collide and stick together. Over time, these pieces grow larger and larger until they eventually form planets.
However, the new research suggests that not all planets form in this way. Some planets, like Psyche, may never be able to fully coalesce into a single object.
"Our findings suggest that there may be more rubble piles in the asteroid belt than we thought," said Becker. "This could have implications for our understanding of how the solar system formed."
